lune777 this is probably referring more to the fact that Rubisco's affinity to bind with O2 and CO2 changes depending on the conditions, and in a sense, these two substates compete to bind to Rubisco's active site. Therefore, the two processes compete with each other. Plus, you're not just going to have one Rubisco enzyme doing all the work in the plant, but rather heaps, so at points, some may bind to O2 and some may bind to CO2. I guess some cells would be undergoing photosynthesis, whilst some may undergo photorespiration depending on the situation. It's all about relative affinity and the levels of substate present. Overall, there will be a swing towards one or the other, and in those hot/dry conditions, there are C4 and CAM plants to accommodate for its negative impacts on Rubisco (i.e. increased photorespiration). I hope that makes sense!

      7 days later

      lune777 no problem! I'm glad it makes more sense. Year 12 photosynthesis and photorespiration stuff can get confusing.

        I saw a diagram and was wondering how a build-up of pyruvate would slow down glycolysis?
        Context: In cellular respiration, if there is an absence of O2 which causes a build-up of NADH (since it can't be converted back to NAD+ in ETC), this would slow down the Krebs cycle, thus there would be a build-up of pyruvate. This build-up causes glycolysis to slow down.

        a month later

        Hi! I had a few questions - I would greatly appreciate any help 🙂

        • If interferon is released and gene expression is paused, isn't this bad for the cell and the organism, as it is unable to produce its own proteins to survive?
        • Does the MHC I represent the proteome of the cell?
        • NK cells kill cells with an abnormal or absent MHC I right - Why might some cells have an absent MHC I marker?

          sarah99 let me see if I can help!

          1. Interferons have antiviral properties, so they're going to try and stop virus replication. In order for viruses to replicate, they're going to take over a host cell and its gene expression machinery, meaning interferons will pause gene expression to prevent viral proteins from being produced (aka preventing viral replication). I'm assuming it would just be preventing gene expression of viral genes, not the cell's genes. That said, the cell would probably have to be cleared from the body anyway because it's already virally infected. The interferons will just prevent the virus from spreading further.
          2. No. The proteome includes all the proteins expressed in an organism. This includes MHC I, but also other proteins in the organism too.
          3. Viruses and tumours/cancerous cells can downregulate the expression of MHC I markers, meaning they can be absent. Some may be present, presenting viral or tumour/cancer peptides (i.e. antigens). Some would function abnormally as well. NK cells will just look to see if normal MHC I markers are being expressed or stressed/abnormal markers, and if there's been any downregulation in the number of MHC I markers.
              9 days later
              2 months later

              For Past exam 2022 question 21 why is multiple choice C is wrong and why is D right like I feel both of them are right

              Hi I'm a bit confused with something I found in a discussion:
              Q: Why is it that once a virus mutates, it isn't recognised by antibodies?
              A: Selection pressures related to it are different. Heamoglutanin and neurominadase help it to enter and leave cells due to antigens and surface proteins - allowing it to go undetected by the immune system.
              Do we need to know about anything in the above answer?

                Also for selective breeding, what does it mean by: you might be inadvertently selecting for an undesirable trait when you’re selecting for certain traits, which is unfavourable for survival.

                  lune777 so answering the first question from what I have from my knowledge so far there's two different types of mutations Antigenic drift and antigenic shift. so for antigenic shift imagine someone is vaccinated for lets say a type of covid strain and there also vaccinated for chickenpox (rlly random) but if those two viruses infect the same host cell (cell in the organism) there a high chance of the two viruses mixing together and basically making a completely new strain now if that happens new antibodies are needed to fight the complete new combination of the two DESPITE the fact that u have been vaccinated for both. and basically a new vaccine is also needed

                      lune777 scientists, researches do make mistakes so they can accidently mess up sometimes and so choose unfavourable traits

                          S007🌿☁️
                          yep this makes sense - i'm just a bit confused about why they were talking about selection pressures and HN proteins.
                          I think they're possibly talking more about antigenic drift occurring (changing Hemagglutinin and neuraminidase) due to viruses with unique proteins that can evade the immune system possibly being selected for, making them more likely to reproduce?
                          Could someone please check this in case it's wrong cos I'm legit just guessing atp lmao

                              S007🌿☁️ ohhh so is this kinda like even though they're selecting for a favourable phenotype, another unfavourable one is also being selected for kinda by accident, that's not better for survival

                                  Hi, just wondering, do plants take in both O2 and CO2 from their environment? I know they release O2 from photosynthesis, but they also need to take in O2 for cellular respiration right? Or do they just use the O2 released from photosynthesis?

                                    sarah99 so plants undergo both cellular respiration and photosynthesis. In photosynthesis, they take in CO2 in the second stage so the Independent stage and then the co2 undergoes carbon fixation and as a result glucose is produced. They also take out oxygen in the light-dependent stage of photosynthesis. Whereas in cellular respiration (aerobic respiration) plants take in oxygen and release carbon dioxide (just like us) and eventually make ATP. I hope that helped.

                                        lune777 no its not better for survival. That's why they have to find new solutions when mistakes like accidentally choosing an unfavorable trait do occur. An analogy for this could be that someone is trying to fix his car or smth he fixed a part of it but then realized he broke another part of the car so now he has to fix that.